A year after China returns rocks from moon’s far side, debate rages over ancient crater
Chinese scientists believe samples found by Chang’e-6 mission answer central question in lunar science, but some in the West have doubts
A year after China returned the first rock samples from the moon’s far side, scientists are debating whether the mission has answered a central question in lunar science – and whether the country’s rising scientific dominance is challenging who gets to tell the story of the moon’s past.
While a team of Chinese researchers believes they may have nailed down the age of the moon’s largest and oldest crater – a colossal impact basin that could hold clues to the early solar system – other scientists, mostly from the West, remain unconvinced.
Some say the ancient rocks may have come from a different impact and were tossed to the landing site. Others suggest the rocks may not have come from an impact at all, but from magma that cooled slowly underground.
“I don’t think the 4.25-billion-year age is 100 per cent certain, but it’s the most credible number we have so far – more reliable than model-based crater counting or meteorites with unknown origins,” said planetary scientist Yang Wei of the Institute of Geology and Geophysics in Beijing.
“It’s based on the only direct evidence we’ve ever collected and measured from the South Pole-Aitken (SPA) basin,” said Yang, who was not directly involved in the study but coordinates a nationwide research effort that gave select teams early access to samples from the Chinese lunar mission Chang’e‑6.
The findings, which he described as the most important among a collection of five papers submitted to the journal Nature for peer review last September, were rejected twice by a review panel dominated by Western scientists.
The paper was later published in National Science Review, a China-based journal. Four others, which detailed the lunar far side’s chemistry, water content and its volcanic and magnetic history, appeared in Nature’s print edition this week.
A Chinese scientist familiar with the review process, who requested anonymity due to the sensitivity of the matter, said he felt some Western scientists were not ready to accept that Chinese researchers might solve such an important scientific problem.
“They didn’t want China to be the one to pin down the age of the SPA basin. Maybe it stings a little,” the scientist said. “But it doesn’t matter. The paper is published, and time will tell.”
In the National Science Review study, researchers from the Chinese Academy of Sciences focused on norite, a type of rock made of two common lunar minerals.
Radiometric dating revealed two distinct age groups of norite particles in Chang’e-6 samples. One was about 3.87 billion years old, consistent with known impact events like Apollo or Schrödinger. The other was much older: 4.25 billion years.
The researchers argued that this older group was likely to have come from the formation of the SPA basin, since the samples were collected from within that basin and no older impact signals were detected. “Our preferred SPA impact age of [around 4.25 billion years] is broadly consistent with crater-counting age estimates from previous studies,” they wrote.
Clive Neal, a planetary geologist at the University of Notre Dame, said the rocks were likely misidentified – not true norites, but impact melts with a similar mineral make-up.
He also noted that the 4.25-billion-year age was significantly younger than what crater-counting models and radiometric data from SPA-linked meteorites had suggested. Neal said the team may have uncovered evidence of a major impact – possibly the one that created the Apollo basin, a crater believed to have formed after the SPA.
Qian Yuqi, a planetary geologist at the University of Hong Kong, said the 4.25-billion-year age was “very close to the lower limit of the SPA basin’s possible age”.
According to a paper Qian and colleagues published in early 2024, extensive intrusive magmatism – a slow, underground process where magma hardens without erupting – is common in the SPA basin. That means the rocks analysed by the Chinese team may not have come from an impact at all.
The five papers emerging from Chang’e‑6 sample analyses revealed a previously untold chapter of the moon’s history – one that, according to Yang, began more than 4.2 billion years ago when a 500km-wide (310-mile) asteroid slammed into the lunar far side.
The impact carved out a colossal basin and melted part of the moon’s deep interior, forming what the researchers call the SPA impact melt rock.
That rock told a story not just of ancient violence, but of surprising resilience. Even after the moon’s mantle was stripped of water and key elements, it somehow erupted again 2.8 billion years ago – possibly triggered by a sudden reawakening of the moon’s magnetic field. “Our work has just started,” Yang said.
Following the Chang’e‑6 mission’s return of nearly 2kg (4.4lbs) of samples from the moon’s far side, the China National Space Administration announced plans to open access to international researchers.
While it may take time to prepare the portions for global distribution, the move could allow for independent testing of one of lunar science’s biggest questions.